The present invention relates to a control arrangement for a cam production machine, for example, a cam milling machine or cam grinding machine for the production of axial curves -- so-called cup or drum cams -- and radial cams or disc cams for oscillating driven levers.
A universally usable cam production machine should be capable of producing cams with as many rising or falling flanks as required in any desired sequence and with any desired swivel angles, associated with the cam flanks of the oscillating layers, and indeed according to a multiplicity of selectable cam laws. In particular, it should also be capable of producing pairs of cam flanks associated to one another for the forced guidance of follower levers, which requires particularly great accuracy. It is desirable to be able to select readily the particular dimensions of a workpiece corresponding to a particular law of the cam profile to be milled, although the law determining data remains fixedly stored in storage means of the machine.
Initially reference will be made to FIGS. 1 and 2 in order to clarify certain terms and relationships, which are well known to those skilled in the automatic machine tool art, and in order to highlight a number of technical problems the understanding of which is a necessary precursor to the understanding of the invention. Referring first to FIG. 1, which shows a cam body which is mounted to be rotatable about a centre of rotation 2. The direction of rotation is indicated by the arrow 3. 4 is the cam profile, which does not necessarily lie on the outer circumference of the cam, but may also be disposed on an internal surface of the cam body. The falling flank 5 and the rising flank 6 are sensed by a roller follower 7, the axis of rotation 8 of which is the centre point of the roller bearing, which is provided on a lever follower 9. The lever 9 is pivotably supported at 10. The points 8 and 10 are connected with one another by the centre line of the lever 9. The centre line of the lever 9 is positioned as indicated at 11 before the roller 7 transverses the falling flank 5 and is positioned at 12 after the roller 7 has traversed the falling flank 5. During such a motion of the lever 9, the axis 8 of the roller 7 passes along an arcuate path 13 and the same path is of course passed through in reversed sequence when a rising flank portion of the cam is traversed by the roller. The reference numeral 14 indicates the angle through the lever 9 is pivotably displaced during the traverse of the path 13. 15 designates the flank angle, i.e. the angular extent of a falling or rising flank. The extreme positions of the axis 8 are connected with one another in FIG. 1 by a straight line 16. The radius of any one point on a flank of the cam body 1 is designated by 17. Explained with reference to FIG. 2 is a special form, in which the take-off does not ensue by means of an oscillating lever, but by means of a linearly guided push rod. The push rod executes a stroke 18 during the traverse of a flank, wherein the centre point of the driven roller runs through a linear path 19.
As is known, one lets falling flanks or rising flanks in control cams take such a course that the spacing between centre of rotation of the cam body and the axis of a roller follower progresses in dependence upon flank angle corresponding to a certain law. There is frequently concerned a connection according to a law representable by a formula, for example that the increase of the stroke of the roller follower over the flank angle take place in accordance with a sine function. This connection of displacement magnitude of a driven member and associated angular extent of a cam is referred to as the law of the cam. For such a cam law, one can produce tables for normalized dimensions, which then contain the co-ordinate pairs for a certain number of so-called support points of the path of motion of the centre point of the driven roller.
There are different possibilities of associating a desired cam law with a certain displacement magnitude, for example stroke height or swivel angle, of the cam gear. FIG. 2 is to be considered once again in this context. It is to be assumed, that the cam law has been considered in the production of the cam in such a manner, that the increase of the cam radius 21 is a function of the increase of the flank angle 20 according to the chosen cam law. The displacement of the push rod follower, which is dependent upon the rotation through the flank angle 20, will then not exactly obey the chosen cam law. The displacement of the push rod will correspond exactly to the chosen cam law only when the cam has been produced by a tool the diameter of which was identical with the diameter of the driven roller, and which was guided according to the cam law on the same linear path, which is later to be traversed by the centre point of the roller follower. Otherwise, distortions result. Similar remarks apply to the arrangement shown in FIG. 1 It is desired, that the swivel angle 14 of the lever follower 9 obeys the desired cam law in dependence upon the flank angle 15. The arc 13, which is traversed by the axis 8 or the centre point of the driven roller 7, corresponds to the swivel angle 14. In a known approximate solution, the cam law is transferred to the notional rectilinear connection 16 of the end positions of the centre point of the driven roller. In this case, the swivel angle 14 obeys a "distorted" cam law. This distortion is very frequently so small, that it is tolerable in practice. In some applications, however, such distortion is unacceptable, for example when cams associated with one another must be produced to generate shape-locked motion. These cams operate without jamming and knocking only when the respective partial angle of the swivel angle 14 or the respective partial arc of the circular arc piece 13 increases exactly according to the desired cam law.
As is known, there are numerically controlled milling machines, which can also be equipped with grinding devices, in which control data can be input to the machine by perforated or magnetic tapes, according to which the individual displacements of the tool carrying and workpiece carrying carriages in co-ordinate pairs can be predetermined. This means, that the co-ordinates actually to be predetermined for the production for a special cam must be calculated support point by support point from tables, which contain normalized co-ordinate pairs for certain cam laws, or with the use of appropriate mathematical formulae. Thereafter, the co-ordinates are stored and afterwards again read out during the production. It is clear, that the entire calculation is to be repeated for cams, which differ from one another in size even though they have the same cam law. The co-ordinates of course arise in such quantities, that the calculation is practically able to be carried out only by a digital calculator. As a result, it takes very long before a cam can actually be produced and one can also not interrupt the work and only undertake slight corrections without the entire calculation having to be repeated. This is a most undesired consequence particularly in the trial stage.
For the determining magnitudes of the cams being given in or modified with little effort even at the cam production machine itself, the control arrangement must have the following properties:
Firstly, the data of the selectable cam laws must be present already stored, i.e. the cam laws must be re-callable. The data of the cam laws will be designated in the following discussion as workpiece-independent data. Secondly, possibilities of input, also for the onput by hand, of data corresponding to the respective workpiece specially to the produced must be present; these data will be designated in the following discussion as workpiece -dependent magnitudes. Thirdly, the control arrangement must finally be able to interlink the stored workpiece-independent data (given from the cam law) with the workpiece-dependent data into control data for individually determinable cams.
In one known cam production machine, the cam laws can be stored in storage means. The cam law can be present as a template or in the form of digitally stored co-ordinate data. The workpiece-dependent determining magnitudes of the cam such as individual cam stroke and individual flank angle, can be predetermined by input means specially provided therefor. A great production flexibility can thus be attained by manual input of data directly into the control arrangement.
With such known cam production machine and its control arrangement, it is however possible only to realize the cam law on the straight line 16 according to FIG. 1, i.e. for an oscillating lever follower of infinite length. In most cases, this inaccuracy does not matter, but there are cases, where one is in fact forced to realize the cam law exactly along the circular arc line 13 according to FIG. 1. It has already been remarked above that this is the case for shape-locked motions such as occur between mutually interacting gears of a gear train.